feat: add bounded protocol fee settlement

[dangelo352]

Summary

• add per-vault ProtocolFeeConfig with bounded fee_bps and fee_recipient
• apply checked, rounded-up protocol fee splitting in both release_funds and redirect_funds
• emit fee_collected for non-zero fees and preserve exact zero-fee settlement behavior
• update ABI metadata, README/backend docs, and add docs/FEES.md

Closes #219

Validation

• cargo fmt --check
• cargo test --test fees -- --nocapture
• cargo test
• cargo clippy --all-targets --all-features -- -D warnings

[1nonlypiece]

thanks for the work here — but our flow is that you need to be assigned to the issue before opening a PR for it. #219 isn't assigned to you, so i'm closing this as invalid for now. please claim #219 first (comment on the issue or grab it on the GrantFox board), then re-raise and we'll review right away. https://discord.gg/xvNAvMJf